Jere Lull wrote:

On 2008-06-20 08:49:34 -0400, Rosalie B. said:

We were motor sailing along snip and I was in the aft cabin when
suddenly it sounded to me as if the engine was running away. Bob
slacked off the throttle and then cautiously came back to speed and the
noise was gone.

This happened about twice more. The gauges never moved during this
time - RPMs were the same, oil pressure normal, engine temperature
normal (and Bob checked that with the infrared gauge), engine charging
as normal. Bob checked the bilges and looked in the engine compartment
and saw nothing amiss. The engine continued to run as normal between
times.

I'm tending towards the alternator idea, but is it possible you picked

The gauges did not change at all.

up a load of weeds? We've done that a few times and it can cause the
vibration, engine loading and lots and lots of black smoke. (Shame you
didn't go back and look). Simply slacking off can sometimes clear most

We did go back and look and saw nothing out of the ordinary (we didn't
look under water of course, but there was no smoke outside of normal).
of it; hitting reverse once or twice certainly will. (the edges of
the
MaxProp blades are pretty sharp.) Plastic bags do the same thing, but
are harder to clear.

It stopped just by coming back to idle. The engine itself wasn't
doing anything out of the ordinary - we looked at it too.

I would find it strange that it would happen a couple of times, but
we've had a pretty fair set of storms recently and it's possible you
were running through some leftover detritus. Particularly if you saw
"rafts" of junk in the vicinity, I'd consider that idea. If not, I'm
not sure.

Another thought: dive on the prop and check for fishing line or
similar, NOT in the marina, of course.

We were in the middle of the Bay. The first time it might have been a
crab pot, but the other times there was no visible debris.

We took the jib and staysail down today so we can haul her and see
what, if anything, is going on. Bob thinks cutlass bearing
deteriorating and letting the prop shaft vibrate. It is about 9 years
old.